Administering fluids containing medicine or nutrients to a patient is well known in the art. Typically, fluid is delivered to the patient by a pump set loaded on a flow control apparatus, such as a peristaltic pump, which delivers fluid to the patient at a controlled delivery rate. A peristaltic pump usually comprises a housing enclosing a rotor or the like operatively connected to at least one motor by a gearbox. The rotor drives fluid through tubing of the pump set by peristaltic action caused by rotation of the rotor driven by the motor. The motor is operatively connected to a rotatable shaft connected to the rotor, which progressively compresses the tubing and drives the fluid at a controlled rate through the pump set. The pump set may have a type of valve mechanism for permitting or preventing fluid flow through the pump set. A controller operates the motor or motors used to drive the rotor and, in some cases, controls fluid flow as by operation of the valve mechanism.
Peristaltic pumps operate by delivering fluid in small charges called “aliquots”. The rotor engages the tubing of the pump set, pinching off a portion of the tubing and pushing fluid ahead of the pinch point (i.e., closer to the patient than to the source of fluid) toward the patient. Typically, the volume of fluid to be administered to the patient is controlled in the pump by counting the number of aliquots, each being of substantially the same volume, and stopping when the number corresponds to a cumulative volume of fluid desired to be delivered. Peristaltic pumps are sanitary and generally highly accurate and therefore very useful in the administration of medication and therapeutic fluids to the patient. However, the accuracy of the pump is dependent upon the dimensional stability of the tubing of the pump set. Over time the pump set tubing can be plastically (i.e., permanently) deformed so that the volume of each aliquot changes. Also, new pump sets can come in various diameters and lengths which can also affect the volume of each aliquot. Therefore, there exists a need for a compensating mechanism to account for the changes in the pump set over time as well as for dimensional variances between pump sets.